DE102011085220A1 - Method and device for detecting sticky deposits during paper production - Google Patents

Abstract

The invention relates to a method and a device for detecting deposits on surfaces of moving machine parts of paper machines. Provision is made for acoustic vibrations generated by the moving machine parts to be recorded and for the recorded vibrations to be evaluated for the presence of deposits on the machine parts.

Description

The invention relates to a method and an apparatus for detecting deposits on surfaces of moving machine parts of paper machines.

For ecological and economic reasons, the use of secondary pulps, that is in particular of waste paper for papermaking, is constantly increasing. Even high-quality graphic and specialty papers are already made from 100% recycled fibers.

In particular, waste papers with functional coatings and waste paper from household-based detection contain increasingly foreign substances, which must be separated before re-paper production. As coarse dirt, foreign materials such as wood, stones, metal, plastic, glass and garbage are found, which are separated by mechanical separation processes at the beginning of the stock preparation process and disposed of. Furthermore, there are films, wet-strength papers and insoluble barrier coatings in waste paper, which should be separated as possible without heavy crushing. This is preferably done in a coarse sorting directly after the material resolution.

In the previous papermaking process introduced paper auxiliaries or subsequently applied functional coatings are removed during recycling and remain partially in the pulp, as well as in the process water, as a complete removal is often not economically feasible. In the further papermaking process, finely dispersed impurities, so-called microstickies, agglomerate into larger particles and pass through the stock preparation without being effectively separated. Coarse-disperse adhesive particles, so-called macro-tricks, likewise pass through the stock preparation and arrive at the paper machine. On contact with adhesive surfaces of the paper machine, stickies deposit and grow to larger contaminants.

If this process of progressive contamination is not detected and stopped in good time, there will be production disruptions, loss of quality and even damage to machine clothing. Since the growth of these impurities sometimes starts due to minor process fluctuations and then proceeds at high speed, the process initially often remains unrecognized.

Paper mills usually operate systems to alleviate this problem. To be on the safe side, overdoses of antibacterial agents that are incorporated into the paper suspension, for example, are the daily practice. This results in unnecessarily high costs for the paper mill.

In stock preparation, larger amounts of sticky can lead to clogging and sticking of separating units. At locations of high turbulence, stickies undergo high shear. As a result, adhering to the surface dirt and filler particles are stripped and the sticky surface is exposed. Elastic deformation results in internal friction, which leads to charge separation and further activation of the stickiness by electrical particle charge. In particular, narrow passages on sorting baskets, nozzles, filters, screens, spray pipes and hydrocyclones, as well as fast rotating components such as impellers, Mahlgarnituren, stirrers, injection jet pumps, etc. could be affected under unfavorable conditions of Stickyablagerungen.

If stickies that have not been separated in the stock preparation, except for the paper machine, deposits are also there. In the so-called constant part of the paper machine, other auxiliaries, such as starch, dye fixatives, sizing agents and other types of specific specialty products, are generally added. The use of these products is often made according to the manufacturer's recommendation with fixed, at best quantitative proportional dosing.

Following the constant part of the supplied pulp comes into contact with the paper machine screen. The pulp is applied through the headbox with a consistency of about 0.5% -1% on the screen. By filtration, a large part of the water is removed, while the solid is largely retained on the screen. To improve the fine and filler retention as well as to accelerate the drainage, chemical aids, so-called retention agents, are added just before the headbox. Their effect is based on flocculation of small particles to larger ones. A true on-demand dosage is usually not possible due to lack of monitoring. While under-dosing of auxiliaries is more likely to be noticed than overdosing due to insufficient process performance, the paper industry tends to be on the safe side and doses more resources than needed. In addition to the increased additional costs for increased use of aids, the consequences of overdosing and residual chemicals in the circulation are difficult to recognize. Not infrequently are cases in which the consequences of an overdose of aids must be compensated by other aids with opposite effect. Apart from high additional costs, the system is slightly unstable and can no longer be controlled reliably.

In non-optimal conditions coagulation of contaminants and stickies is possible. If charge and temperature fluctuations coincide with a high proportion of potential sticky substances in the substance, stickies are precipitated and deposited on machine parts. The hydrophobic surfaces of stickies causes small particles to aggregate to larger ones. Stickies grow to partly large fabrics. The process often begins with clothing (wet and dry sieves and press felts). On contact with external rollers, stickies are transferred to their surface, where they form ring or lumpy deposits. If the rollers are not cleaned, the coating can lead to the bleeding and destruction of clothing. Deposits on formation sieves lead to disruption of the leaf structure, as no uniform leaf formation is possible in the affected areas. Light stains and thinner sheet thicknesses affect both strength and optical properties and processing properties.

To remove the Stickys or to avoid the growth of Stickys various methods are known. Thus, for example, mechanical scrapers are provided on numerous paper-making machines for numerous rolls and drying cylinders. Here, a blade is placed against the direction of rotation of the roller or the cylinder at an acute angle and pressed with high pressure on the surface. Deposits, for example sticky deposits on the surface, are lifted off in a spatula method and collected on the scraper. The high mechanical Anpressköpfe cause a strong braking effect, which must be additionally provided by the paper machine drives. By this scraping resulting particles can get into the paper web and lead there to holes, breaks or tension.

The object of the invention is to provide a method and a device by means of which an early detection of sticky deposits on rollers, cylinders, clothing or the like is possible in a simple and secure manner.

According to the invention, we achieved the object by a method having the features mentioned in claim 1.

According to the invention, it is provided that deposits on machine parts of paper machines are detected by means of acoustic measurements. In this case, the fact is utilized that in particular the deposits which slide through under a scraper or the like, in particular sticky deposits, generate vibrations or noises. These vibrations can be detected and evaluated by acoustic detectors.

It is particularly advantageous that already an incipient deposit is reliably detected. At this time, a targeted countermeasure can be taken.

In particular, it is also advantageous that the deposits are recognized when they actually occur. This makes it possible in particular to avoid overdosing of excipients, which should avoid later sticky deposits. Furthermore, the formation of deposits can be detected in good time so that expected damage to the paper machines or quality impairments of the paper produced can still be avoided. It is thus possible to detect Stickyablagerungen beginning at an optimal time or at an optimal location and thus be able to take appropriate countermeasures efficiently.

The object is further achieved by a device having the features mentioned in claim 6.

It is particularly preferred if at least two acoustic transducers are present, which are arranged in particular over the width of a paper web to be produced. As a result, by means of the signals measured by means of the at least two acoustic transducers, by means of evaluating transit time differences of the signals, it is possible to determine exact location information for the development of sticky deposits. By means of a frequency evaluation and / or an amplitude evaluation as well as additionally with several acoustic transducers over a transit time comparison of the signals, a multiplicity of different measuring tasks can be realized according to the invention.

In particular, it is now possible to make reliable predictions about impending deposition of adhesive contaminants. Thus, the connection between the presence of potentially adhesive constituents in the pulp or circulation water and triggering factors for deposition and the actual deposition in the material system or on components of the paper machines can now also be established. Compared to visual monitoring by trained machine personnel, complete monitoring of the deposit of stickies can now be achieved. Since this deposition occurs very sporadically and then rapidly progressing, can thus be taken immediately by the permanent monitoring.

It is therefore possible, the affected machine parts by an automated measuring system permanently monitored and to detect the first signs of incipient occupancy of machine parts with Stickyablagerungen and bring to the display. The corresponding countermeasures can then be triggered immediately.

The invention will be explained in more detail in an embodiment with reference to the accompanying drawings. Show it:

1 a schematic side view of a measuring arrangement according to the invention;

2 a schematic plan view of the measuring arrangement according to the invention, and

3 a clarification of the measuring principle.

In 1 is a roller 10 a not shown in detail paper machine shown. About the roller 10 runs an indicated here paper web 12 from a upstream station to a downstream station. At the roller 10 it may be a guide roll, a drive roll or, for example, a drying cylinder or the like.

The roller 10 is a scraper 14 assigned, by means of which a surface 16 the roller 10 should be cleaned. The scraper 14 is also used in particular, so-called Papierumwickler when tearing the paper web 12 to prevent.

On the scraper 14 are two acoustic vibration sensors 18 and 20 arranged. The vibration sensors 18 and 20 are with an evaluation and control circuit 22 connected.

In 2 are on the surface 16 the roller 10 indicated starting sticky deposits 24 indicated. These adhere to the surface 16 and rotate with the roller 10 With.

Through this rotation the Stickyablagerungen get 24 in contact with the longitudinal extent of the roller 10 extending edge 26 the scraper 14 , Upon impact of Stickyablagerungen 24 on the scraper 14 An acoustic vibration is generated by structure-borne sound signals within the scraper 14 is transmitted. The on the scraper 14 arranged vibration sensors 18 and 20 detect these vibration signals. About the evaluation circuit 22 can according to a frequency evaluation and / or an amplitude evaluation of the vibration signals on the size and number of Stickyablagerungen 24 getting closed.

The vibration signals are within the scraper 14 evenly transmitted, so these from the vibration sensors 18 and 20 according to the distance to the occurrence of Stickyablagerung 24 be received at different times. Over a runtime comparison of the signals can be so on a specific location of Stickyablagerungen 24 on the roller 10 getting closed.

In 3 this measuring principle is clarified. Schematically indicated as a Stickyablagerung 24 on the edge 26 the scraper 14 occurs. According to the random distribution of sticky deposit 24 on the surface 16 the roller 10 is the place of Stickyablagerungen 24 unpredictable. By hitting a certain point of the edge 26 Starting from this point, the structure-borne sound signals within the scraper 14 transmitted and from the vibration sensors 18 and 20 detected. The vibration sensors 18 and 20 have a fixed position on the scraper 14 , This results in a defined distance A between the vibration sensors 18 and 20 , Corresponding to the point on the edge 26 at the sticky deposit 24 this point is located at a distance I1 from the vibration sensor 18 and a distance I2 from the vibration sensor 20 , It becomes clear the nearer the point of the edge 26 is where the sticky deposit is 24 on the scraper 14 occurs, to those of the vibration sensors 18 . 20 is, the shorter is the distance I to the arrangement points of the vibration sensors 18 and 20 , The shorter the distance I, the sooner the generated structure-borne sound signal is received and the evaluation circuit 22 transmitted. According to the example shown, this is done via the vibration sensor 18 Detected structure-borne sound signal earlier in time at the evaluation circuit 22 arrive as the from the vibration sensor 20 detected structure-borne sound signal. Due to this difference in transit time can due to the known fixed distance A between the vibration sensors 18 and 20 and the known geometrical size of the scraper 14 on the impact point of Stickyablagerung 24 on the edge 26 getting closed.

In summary, it can thus be stated that with the measuring arrangement according to the invention an incipient sticky deposit can be reliably detected. At the same time a rapidly progressing contamination is recognizable. By one of Stickyablagerungen 24 generated typical structure-borne sound signal can be distinguished from other recorded structure-borne sound signals, for example due to vibrations of the paper machine or machine parts of the paper machine itself. The measurement can be carried out permanently, that is, online, so that remote monitoring and corresponding reactions can be initiated immediately upon detection of a sticky deposit. From a critical size, this can include, for example, automatic surface cleaning or stopping the paper machine. Also can be done by the quasi-real-time detection of Stickyablagerungen 24 be optimally intervened in the above process by appropriate countermeasures, such as addition of agents to prevent Stickyablagerungen be dosed more accurately. The entire papermaking process is not affected or impaired by the measuring arrangement. The measurement data can be archived in a simple manner and thus assigned to the corresponding batch produced the paper web. As a result, improved quality control is possible in a simple manner.

The simple structure results on the one hand a robust operation and on the other hand easy maintenance and repair.

Thus, the affected machine parts of a paper machine can be permanently monitored by an automated measuring system to detect the first signs of an incipient occupancy of machine parts with deposits and bring to the display.

LIST OF REFERENCE NUMBERS

10

roller

12

paper web

14

scraper

16

surface

18

vibration sensor

20

vibration sensor

22

evaluation

24

Sticky deposit

26

edge

A

distance

Claims (10)

Method for detecting deposits on surfaces of moving machine parts of paper machines, characterized in that the vibrations generated by the moving machine parts are detected and the detected vibrations are evaluated for the presence of deposits on the machine parts. A method according to claim 1, characterized in that the vibrations are permanently detected. Method according to one of the preceding claims, characterized in that the vibrations are detected by means of vibration sensors, which are mechanically coupled to the machine parts or with the machine parts in contact-engageable devices. Method according to one of the preceding claims, characterized in that the vibrations are evaluated on their frequency response and / or amplitude characteristic. Method according to one of the preceding claims, characterized in that at least two vibration sensors are provided, and the signals supplied by the at least two vibration sensors are evaluated for accurate location of a deposit on their runtime behavior. Device for detecting deposits on surfaces of moving machine parts of paper machines, characterized by at least one vibration sensor ( 18 . 20 ), which is connected to the machine part ( 10 ) or one with the machine part ( 10 ) contactable device ( 14 ) and one with the at least one vibration sensor ( 18 . 20 ) connected evaluation circuit ( 22 ). Apparatus according to claim 6, characterized in that at least two vibration sensors ( 18 . 20 ) are provided. Apparatus according to claim 7, characterized in that the at least two vibration sensor ( 18 . 20 ) are arranged at a defined distance A from each other. Device according to one of the preceding claims, characterized in that the moving machine part is a guide roller, a drive roller, a screen cloth, a drying cylinder, a drying wire, a clothing means or the like. Device according to one of the preceding claims, characterized in that the device is a scraper ( 14 ).

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